The formula weight and exact mass are averages based on the polydispersity of PEG.
PEG-modified lipidsare typically added to phospholipid vesicles used for drug deliveryto provide a steric coating on the surface of the membrane to hinder clearing of the particles by the reticuloendothelial system (RES). This prolongs the circulating plasma half-life of the drug. The plasma half-life of the drug can be "tuned" from several hours to days depending on the size of the PEG and fatty acids attached to the lipid anchor.